Natural circulation in an enclosed rod bundle of large aspect ratio

Highly turbulent natural circulation in an enclosed tall rod bundle is investigated using Large Eddy Simulation (LES). The consists of 36 heated rods and insulated central tubeenclosed by a cooled containment wall. This geometry directly relevant to nuclear fuel bundles generic heat exchangers. For bundles, importance accident scenarios. A 60° azimuthally periodic sector the modelled. Rayleigh number based on height 7.6×1012 1.23×1013 for two cases studied. flow, turbulence, thermal characteristics system show strong distinct features top, middle, bottom regions (about 0.2, 0.6, 0.2 splits), which are strongly influenced vertically developing buoyancy-driven boundary layer surface. flow top region largely stagnant with stratification weak cross flow. laminar however formed wall later transitions turbulence. turns out be dominant feature bundle. velocity profile transfer this well represented, respectively, similarity solution well-established Nusselt correlation unconfined flat plate. In middle-height region, can naturally split into outer zone. former resembles simple, rectangular, asymmetrically heated/cooled cavity, represented convection correlation. zone mixed upwards pipe/channel though entrainment fluid from means that accelerates axially until middle-height. Irrespective differences zones, near-wall behaviour fields shows at different heights as between zones. They also shown consistent flows simple geometries. dominated impinging jet resultant inner one.